Project Summary: Medulloblastoma (MB) is the most common malignant brain tumor in children. Treatment for MB includes surgery, radiation and chemotherapy. Unfortunately, long-term morbidity, including lifelong cognitive deficiencies, endocrine dysfunction, neurological defects, emotional and social problems, and secondary tumors are associated with current treatments. Such treatment associated side effects are particularly evident in children, as their brains are still growing, and they can survive many years after treatment. MB is a heterogeneous disease with at least 12 different subgroups identified. Patients with high MYC expressing MB (25-30% of cases; referred to as Group3) have the worst prognosis (survival at 5 years is 41.9% in the Group 3? subtype), and MYC is known to be a major driver of this MB subtype. Thus, for Group 3 MB there is a pressing need to develop novel targeted therapies that confer limited toxicities. However, MYC has remained ?undruggable?. To identify novel therapeutic targets in high MYC expressing MBs, we have begun to examine the role of the EYA2 transcriptional co-factor and dual phosphatase (Tyr and Ser/Thr in separable domains) in MB progression. Intriguingly, EYA2 has been shown to control MYC, both transcriptionally and post- translationally, during embryonic development, but is normally downregulated after development is complete. Our preliminary data show that EYA2 is overexpressed in Group3 MB compared to normal cerebellum and other subtypes of MB, that it controls MYC levels in the context of Group3 MB, and that KO of EYA2 dramatically diminishes in vivo growth of Group3 MB. Our main objective in this proposal is to identify novel druggable targets in Group 3 MB; targets that when inhibited will not lead to the significant side effects associated with current MB therapies. To this end, we will test the hypothesis that the SIX1/EYA2 transcriptional complex and/or EYA2 phosphatase plays a critical role in Group 3 MB progression via transcriptionally activating and/or stabilizing MYC, and that novel inhibitors targeting the activity of EYA2 can diminish disease progression while conferring limited side effects. To address this hypothesis, we will carry out three aims: 1) Determine which activity of EYA2 regulates MYC and contributes to the aggressive nature of Group 3 MBs, 2) Determine if regulation of MYC by EYA2 is required for its effects on MB growth and progression, 3) Determine whether EYA2 inhibition, genetically or pharmacologically (using novel small molecule inhibitors targeting either its transcriptional activity with SIX1 or its Tyr phosphatase activity), will provide a unique means to inhibit the critical oncogene, MYC, preventing MB progression in vivo. If our hypothesis is correct, and EYA2 is a key, druggable regulator of MYC, we will have identified an achilles heel not only for Group3 MB, but potentially for the many other MYC-dependent tumors. Targeting MYC remains a ?holy grail? in cancer research, and our studies seek to do so via a novel means anticipated to have limited toxicity due to the paucity of EYA2 expression in normal tissues after development is complete.